Sorbents for carbon dioxide reduction from indoor air

ABSTRACT

A sorbent for CO 2  reduction from indoor air from an enclosed space. In some embodiments, the sorbent comprises a solid support and an amine-based compound being supported by the support. The sorbent captures at least a portion of the CO 2  within the indoor air. The sorbent may be regenerated by streaming outdoor air through the sorbent to release at least a portion of the captured CO 2 . The sorbent is structured to allow indoor air to flow therein with relatively low flow resistance and relatively rapid reaction kinetics. Regeneration may be performed at relatively low outdoor air temperatures, thereby minimizing the thermal energy required for regenerating the sorbent.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/117,797, having a 35 U.S.C. 371(c) date of Jun. 20, 2014, now U.S.Pat. No. 9,533,250, which is U.S. National Phase application, filedunder 35 U.S.C. §371(c), of International Application No.PCT/US2012/038343, filed May 17, 2012, which claims priority to PCTPatent Application No. PCT/US2011/036801, filed May 17, 2011, andentitled “Method and System for Improved-Efficiency Air-Conditioning,”and U.S. Provisional Patent Application No. 61/575,577, filed Aug. 23,2011, and entitled “Removal of Carbon Dioxide from Indoor Air UsingAmine-Impregnated Solid Adsorbents.” The disclosures of each of theabove applications are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present application generally relates to sorbents for reduction ofsubstances from air and in particular to sorbents for reduction ofcarbon dioxide from indoor air.

BACKGROUND

Amines are organic compounds and functional groups that contain a basicnitrogen atom with two or less hydrogen atoms. Primary amines have twohydrogen atoms attached, secondary amines have one hydrogen atom. Aminesare derivatives of ammonia, wherein one or more hydrogen atoms have beenreplaced by a substituent such as an alkyl or aryl group.

Amine gas treating is a well known process in the art using variousforms of amines to remove carbon dioxide (CO₂) from gases present inrefineries, petrochemical plants and natural gas processing plants.

Removal of CO₂ from controlled, sealed environments (submarines,spacecrafts or space suits, and the like) is also known in the art.

SUMMARY

There is thus provided in accordance with an embodiment of the presentdisclosure a sorbent for CO₂ reduction from indoor air. The sorbentcomprises a solid support and an amine-based compound attached to thesupport. The sorbent captures at least a portion of the CO₂ within theindoor air. The sorbent may be regenerated by streaming outdoor airthrough the sorbent to release at least a portion of the captured CO₂.The sorbent is structured to allow indoor air to flow therein withrelatively low flow resistance and relatively rapid reaction kinetics.Regeneration may be performed at relatively low temperatures, therebyminimizing the thermal energy required for regenerating the sorbent.

According to some embodiments of the present disclosure, there isprovided a sorbent for reduction of CO₂ from indoor air of an enclosedspace. The sorbent includes a solid support and an amine-based compoundsupported by the support. The amine-based compound is provided tocapture at least a portion of the CO₂ within the indoor air and releaseat least a portion of the captured CO₂ by streaming outdoor air throughthe sorbent. The support may include a porous solid material or a fineparticle solid material. The support may include a clay. The support mayinclude a plurality of particles, and in some embodiments, the pluralityof particles have an average diameter dimension in the range of 0.1-10millimeters, 0.2-3 millimeters, or 0.3-1 millimeters. In someembodiments, the amine-based compound includes at least 50% or 25%secondary amines.

According to some embodiments, the support is initially in the form offine particles and is mixed with an anmine-based compound, andthereafter formed as a plurality of particles. In some embodiments, thesupport includes particles, fine particles, or a powder based solid,wherein the fine particles are agglomerated into larger particles so asto facilitate air flow through the sorbent.

According to some embodiments of the present disclosure, there isprovided a method for reducing CO₂ from an enclosed environment. Themethod includes providing a sorbent and a support for the sorbent, thesorbent includes an amine-based or amine-like compound; streaming afirst gas containing CO₂ from inside an enclosed environment through thesorbent such that the sorbent captures at least some of the CO₂ of thefirst gas; and streaming a second gas containing less CO₂ than the firstgas from outside the environment through the sorbent such that thesorbent releases at least some of the captured CO₂ to the second gas.The enclosed environment may be a private, public, residential, orcommercial space. The first gas may be indoor air and/or the second gasmay be outdoor air. The method may further include providing the sorbentand the support in communication with a heating, ventilation, and airconditioning (HVAC) system. In some embodiments, the HVAC system isconfigured to stream the second gas through the sorbent.

According to some embodiments, a system for reducing CO₂ contained inair from an enclosed environment is provided where the system includesan HVAC system and a sorbent in communication with the HVAC system. Thesorbent includes a solid support, and an amine-based compound beingsupported by the support. The HVAC system is configured to flow indoorair over and/or through the sorbent and the amine-based compound isconfigured to capture at least some of the CO₂ within the indoor air. Inaddition, the HVAC system is configured to flow outdoor air over and/orthrough the sorbent such that at least a portion of the CO₂ captured bythe sorbent is released therefrom.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The principles and operations of the systems, apparatuses and methodsaccording to embodiments of the present disclosure may be betterunderstood with reference to the drawings, and the followingdescription. These drawings are given for illustrative purposes only andare not meant to be limiting.

FIG. 1 is a schematic illustration of a sorbent construct according tosome embodiments of the present disclosure;

FIG. 2 is a graph showing the operation of the sorbent construct duringadsorption of CO₂ according to some embodiments of the presentdisclosure;

FIG. 3 is a graph showing the operation of the sorbent construct duringregeneration of the sorbent construct according to some embodiments ofthe present disclosure;

FIG. 4 is a graph showing the operation of the sorbent construct duringadsorption of CO₂ according to some embodiments of the presentdisclosure;

FIG. 5 is a graph showing the operation of the sorbent construct duringregeneration of the sorbent construct according to some embodiments ofthe present disclosure; and

FIG. 6 is a graph showing the operation of the sorbent construct duringadsorption of CO₂ according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 is schematic illustration of a sorbent construct, according tosome embodiments of the present disclosure. As seen in FIG. 1, a sorbentconstruct 100 (which may also be referred to as a filter or scrubber,for example) may be in fluid communication with indoor air from anenclosed environment 102.

The enclosed environment 102 may be, for example, an office building, acommercial building, a bank, a residential building, a house, a school,a factory, a hospital, a store, a mall, an indoor entertainment venue, astorage facility, a laboratory, a vehicle, an aircraft, a ship, a bus, atheatre, a partially and/or fully enclosed arena, an education facility,a library and/or other partially and/or fully enclosed structure and/orfacility which can be at times occupied by equipment, materials, liveoccupants (e.g., humans, animals, synthetic organisms, etc.) and/or anycombination thereof.

Indoor air within and around buildings and structures is affected by aplurality of substances, comprising contaminants. Among thesecontaminants, usually with the highest concentration, is CO₂. There areother contaminants, such as carbon monoxide, nitrous oxides and sulfuroxides, which may appear in relatively lower concentrations. Anotherclass of such contaminants is a group of species of organic vapors,broadly referred to as Volatile Organic Compounds (VOC). The sources ofthese vapors include, inter alia, the human occupants themselves—fromrespiration and perspiration to clothing and cosmetics—as well asbuilding materials, equipment, food and consumer products, cleaningmaterials, office supplies or any other materials emitting VOCs.Additional contaminants may be microorganisms including, inter alia,bacteria, viruses and fungi and airborne particles.

In a human occupied enclosed environment 102, the concentration of CO₂within the indoor air is typically in the range of 400-5000 parts permillion (ppm). Additionally, the concentration of CO₂ in the indoor airmay be in the range of 400-2000 ppm. Moreover, the concentration of CO₂in the indoor air may be in the range of 500-1500 ppm. Furthermore, theconcentration of CO₂ in the indoor air may be in the range of 800-1200ppm.

The concentration of CO₂ in outdoor air, external to the enclosedenvironment 102, is typically in the range of 300-500 ppm. Higher levelsmay be seen in the vicinity of combustion or living organisms. There areconcerns about a continual increase in atmospheric CO₂ levels, soatmospheric levels may be higher in the future.

In some embodiments the concentration of CO₂ in outdoor air may be lowerthan in the indoor air by a range of 100-2000 ppm. Additionally, theconcentration of CO₂ in outdoor air may be lower than in the indoor airby 1200 ppm or less. Furthermore, the concentration of CO₂ in outdoorair may be lower than in the indoor air by 800 ppm or less.Additionally, the concentration of CO₂ in the outdoor air may be lowerthan in the indoor by 400 ppm or less.

The sorbent construct 100 is provided to reduce the concentration ofsubstances present therein by scrubbing the substances from indoor air114. The sorbent construct 100 may comprise a sorbent 120 that iscomposed of at least two functional groups of materials: a passivesupport and an active compound. The support materials generally providethe mechanical and physical structure of the sorbent and the activecompound attracts and captures CO₂.

Following the capture of the substances, the sorbent construct 100 maybe regenerated by urging the release of at least a portion of thesubstances, such as CO₂, therefrom. Regeneration is a very importantaspect of sorbent performance and often the step where the most energyis required, as described hereinbelow.

Regeneration may be performed by a combination of heating, purging,pressure change, electrical energy, and/or any combination thereof.Additionally, the release of substances can be achieved by a combinationof heating and purging with air or other purge gas. The releasedsubstances may be expunged into the atmosphere or otherwise collected,disposed of, sequestered, and/or any combination thereof.

In accordance with some embodiments the regeneration may be performed bystreaming purge gas 124 through the sorbent construct 100 for release ofat least a portion of the substances, such as CO₂, therefrom. Ideallysuch incoming purge gas would have very low CO₂ concentrations. Althoughoutdoor air contains an amount of CO₂, use of outdoor air as a purge gas124 for regeneration of the sorbent construct 100 may be advantageousdue to the availability and cost efficiency of outdoor air. Inaccordance with some embodiments the CO₂ concentration of the outdoorair may be smaller by any amount than the CO₂ concentration of theindoor air for allowing the outdoor air to purge and thus regenerate thesorbent 120.

The purge gas 124 may be introduced into the sorbent construct 100 at asuitable temperature for effective regeneration, such as in the range ofapproximately 20-200° C. In accordance with some embodiments thetemperature of the purge gas 124 is relatively low such as lower than100° C., or in the range of approximately 30-80° C., or as low as in therange of approximately 30-60° C. Accordingly, if outdoor air is used aspurge gas it may be required to be relatively minimally heated, or inaccordance with some embodiments, may be introduced into the sorbentconstruct 100 without any prior heating.

The purge gas 124 may comprise air, outdoor air, indoor air, N₂ acombination thereof or any other suitable gas. In one preferredembodiment, outdoor air is used as purge gas.

The support component of the sorbent 120 may be formed of any suitablematerial. In a non-limiting example the support may be formed ofgenerally chemically inert materials. Additionally, the support may beformed of adsorbent materials, such as gels, molecular sieves,nanotube-containing materials, porous materials, fiber based materials,sponge-like materials, electrically and/or electro-magnetically chargedliners or objects, porous organic polymers, any other chemical,biological attractants, and/or any combination thereof. The adsorbentmaterials may comprise ion exchange resins, polymeric absorbent resins,acrylic ester polymers, polystyrene divinyl benzene, polymethylmethacrylate (PMMA), polystyrene, styrene divinylbenzene (SDB), fly ash,carbon, activated carbon, carbon nanotubes, or alumina nanoparticles,for example. Additional porous materials may comprise zeolite, syntheticzeolite, porous alumina, porous minerals, silica, porous silica, silicananoparticles, fumed silica, activated charcoal and metal organicframeworks, for example. An additional porous material may be clay,including aluminum phyllosilicates such as bentonite, montmorillonite,ball clay, fuller's earth, kaolinite, attapulgite, hectorite,palygorskite, saponite, and sepiolite, for example.

In some embodiments, the support may comprise a combination of severaldifferent adsorbent materials.

Some of these materials may be available from a variety of commercialsources, such as from BASF SE of Ludwigshafen, Germany; Clariant SE ofFrankfurt am Main Switzerland, Europe; The Cabot Corporation of Boston,Mass., USA, and Evonik Industries of Essen, Germany, for example.

The support may be formed in any suitable configuration, such as a solidsupporting substrate or solid support formed with a relatively largetotal surface area. The solid support may comprise any suitable materialwhich is not a liquid. For example, the solid support may be formed of aplurality of elements such as solid particles 130 or sheets, forexample. The total surface area may be generally defined as the sum ofthe surface areas of each element forming the solid support.

In FIG. 1 exemplary particles 130 are shown. The particles 130 may beconfigured in any suitable shape or method such as powders, fibers,granules, beads, pellets, extrudates or a combination thereof. Thefibers may be any suitable fiber such as carbon fiber, silica fibers orpolymer fibers, for example. The fibers may be weaved or intertwined toform a fabric or a paper-like material.

The fibers, granules, beads, pellets and extrudates may be formed of anysuitable material as described hereinabove. The support may be formed ofa plurality of thin sheets. The sheets may comprise natural or syntheticfiber based materials, paper, natural fabrics, or synthetic fabrics. Thesheets may be formed in any suitable size, such as with a thickness inthe range of approximately one micron to two centimeters. Additionally,the range may be approximately 2-80 millimeters, for example. In someembodiments the sorbent 120 may comprise a large surface area (such asthe total surface area of the plurality of particles 130), for examplein the range of 10-1000 square meters per gram.

The particles 130 may be formed with dimensions ensuring that theparticles 130 are not too fine thereby forming an overly dense layer,which may prevent the flow of the indoor air 114 through the sorbentconstruct 100. Additionally the particles 130 may be formed withdimensions ensuring that a total surface area of the plurality ofparticles 130 is sufficiently large for allowing the indoor air 114 tohave maximal contact with the particles 130 for maximal adsorption ofthe substance, such as the CO₂.

In a non-limiting example, the average diameter of the particles 130 maybe in the range of approximately 0.1-10 millimeters. Not all particlesare likely to be identical in shape and size, therefore the typical oraverage particle comprises an average of an aggregate of such particles.In another non-limiting example, the average diameter of the particles130 may be in the range of approximately 0.2-3 millimeters. In yetanother non-limiting example, the diameter of a particle 130 may be inthe range of approximately 0.3-1 millimeters. The diameter of theparticle 130 may be measured as the approximate diameter, wherein theparticle is a granule or bead, or may be measured as a cross sectiondiameter, wherein the particle is a fiber, an extrudate or a pellet.

The sorbent 120 may be arranged in any suitable manner. For example, thesorbent 120 may be placed within an enclosure 140 formed in any suitableconfiguration. The particles 130 or thin sheets or any other sorbent 120may be relativity densely packed within the enclosure 140 at a densityallowing the indoor air 114 to have maximal contact with the particles130 for maximal interaction therefrom yet not overly dense, which mayprevent the flow of the indoor air 114 through the sorbent construct100.

Exemplary enclosures 140 and air treatment modules are disclosed inapplicant's US Publication No. 20110198055, which is incorporated hereinby reference in its entirety.

The active compound in the sorbent 120 may be an amine-based oramine-like compound. The amine compound is suitable for adsorbing CO₂present in the indoor air 114. The amine-based compound may comprise anysuitable amine, such as a primary or secondary amine, or a combinationthereof. Additionally, the amine-based compound may range fromrelatively simple single molecules, such as ethanolamine, to largemolecule amino polymers such as polyethylenimine. The amine-basedcompound may comprise monoethanolamine (MEA), ethanolamine, methylamine,branchedpolyethyleneimine (PEI), linear polyethyleneimine (PEI),diethanolamine (DEA), dimethylamine, diethylamine, diisopropanolamine(DIPA) tetraethylenepentamine (TEPA), methyldiethanolamine (MDEA),methylethanolamine, and any of a number of polyamines such aspolyethylenimine, or a combination thereof, for example.

The amine-based compound may be liquid or solid or any other suitablephase.

It is known in the art that amines selectively capture a relativelylarge amount of CO₂. As described hereinabove, the sorbent construct 100is employed to reduce substances, such as CO₂, within the indoor airexiting the enclosed environment 102. Indoor air typically comprises arelatively low concentration of CO₂, ranging from 400-2000 ppm. Thus useof an amine-based compound is highly effective in reducing theconcentration of CO₂ within indoor air. Additionally, indoor air iscomposed of other gas compounds, predominantly about 75-82% or 79-82%Nitrogen; and 15-21% or 18-21% Oxygen. Water may also be presentdepending on the humidity level of the indoor air. For example, theremay be a presence of 0%-5% water in the indoor air. Therefore it isadvantageous to use an amine-based compound which allows selectivecapturing of the CO₂, and possibly other substances, while avoidingsaturation of the sorbent construct 100 with water or the other indoorair gas compounds. An example of CO₂ adsorption by an amine-basedcompound supported by a solid support is described in reference to FIGS.2, 4 and 6.

In accordance with some embodiments the amine-based compound maycomprise a relatively large fraction of secondary amines. In someembodiments like diethanolamine, the amines are 100% secondary amines.In other embodiments, like certain polyamines, between 25%-75% of aminesare secondary amines. Additionally, the amine-based compound maycomprise at least 50% secondary amines. Moreover, the amine-basedcompound comprises at least 25% secondary amines.

Primary amines, which comprise NH₂ elements, create strong chemicalreaction with CO₂. Secondary amines, which comprise a single hydrogen,i.e. NH, create weaker chemical reaction with CO₂ yet still efficientlyand selectively capture the CO₂. Accordingly, secondary amines requireless energy for releasing the captured CO₂ therefrom than the energy(such as thermal energy) required for releasing CO₂ from primary amines.The more-readily releasing secondary amines allow satisfactory capturingof the CO₂ from indoor air while also allowing relatively rapid and lowenergy regeneration of the sorbent 120. Accordingly, regeneration of thesorbent 120 may be performed by relatively low-temperature using outdoorair. The ability to regenerate the sorbent with minimal added heat ishighly advantageous for treating indoor air.

As described hereinabove, the sorbent 120 may be formed of particles130, thin sheets or any configuration which provides a relatively largetotal surface area for contact with substances. This amine-containingsolid sorbent allows the indoor air 114 to have maximal contact with theamine-based compound for maximal CO₂ removal from the indoor air. Thisis advantageous for indoor air which typically has a low concentrationof CO₂, as described hereinabove. Additionally, use of theamine-containing support with a relatively large total surface areaallows disposing the sorbent construct 100 within a relatively compact,small sized enclosure 140.

Additionally, the sorbent 120 may be formed of particles 130, thinsheets or any structure which is permeable to a gas flowing throughsorbent 120 with relatively low flow resistance. The particles 130 andthin sheets allow the indoor air to readily flow between the particles130 or sheets. As described hereinabove, the sorbent 120 may be formedof porous materials thereby allowing the indoor air to also flow throughthe particles 130 or sheets and thus enhancing the gas permeability ofthe sorbent 120.

Moreover, the sorbent 120 structured with a relatively large totalsurface area and with relatively high fluid permeability provides forrelatively rapid reaction kinetics and thus a relatively large quantityof CO₂ is captured quickly by the amine-containing support. Reactionkinetics or chemical kinetics may be defined as the rate of a chemicalprocess, such as the rate the CO₂ is captured by the sorbent 120.

Low flow resistance and rapid reaction kinetics is advantageous forcapturing CO₂ from indoor with a relatively low CO₂ concentration.

Low flow resistance and a relatively large total surface area of thesorbent 120 also allows the purge air 124 to readily release the CO₂from the sorbent 120, as explained hereinabove. Consequently, the purgeair 124 may regenerate the sorbent with minimal added heat in arelatively short time and additionally the purge air 124 may compriseoutdoor air.

Examples of chemically inert supports with a large total surface maycomprise clay, silica, metal oxides like alumina, or a combinationthereof. For example, acid-treated bentonite clay chemically binds wellwith the hydroxyl group of diethanolamine (DEA) to form a stablesorbent; it is known in the art that polyethylenimines (PEI) attach tosilica surfaces, thereby, these supports and amine may be used as asorbent for selective and efficient CO₂ removal from indoor air.

An example of large surface area solids carrying liquid amines isdescribed by Siriwardane (U.S. Pat. No. 6,908,497), where bentonite clayis impregnated with an amine, resulting in amine impregnated clay thatacts as a selective adsorbent of CO₂.

The amine-containing sorbent may be synthesized in any suitable method,known in the art. In a non-limiting example, a solid support may beimpregnated by the amine-based compound in any suitable manner, such asby spraying, dripping or immersion within a solution of the amine-basedcompound, for example. The impregnation may additionally oralternatively be mechanically stimulated, with catalysts, or withexternal energy sources, such as heat.

In accordance with some embodiments, the solid support may initiallycomprise particles, which are thereafter impregnated by an amine-basedcompound, as described hereinabove and as exemplified in example 1.

In accordance with other embodiments, the solid support may initiallycomprise fine particles, such as a powder. The fine particles may bemixed with the amine-based compound, such as by immersion of the fineparticles in an amine-containing liquid or solution to form anamine-containing powder for example, as described in example 2.

In accordance with other embodiments the amine-containing powder isagglomerated to form the support by standard procedures, such asgranulation for forming granules or beads and pelletization or extrusionfor forming pellets or extrudates, for example, as described in example3.

If solvents are used in the process of synthesizing the support and theamine, the resulting sorbent may need to be dried in any suitablemanner.

The amine-based compound may be a liquid, a solid or may be initially asolid solved in a solvent. For example, a solved amine-based compoundmay comprise diethanolamine (DEA), which may be solved in any suitablesolvent such as Dichloromethane (DCM). Additionally, the solvedamine-based compound may comprise polyethyleneimine (PEI), which may besolved in any suitable solvent, such as water, ethanol, methanol,ethylene glycol (EGW) or propylene glycol (PGW), for example.

The conditions and parameters for forming the amine-containing supportmay vary according to the properties of the selected support and theselected amine-based compound.

The sorbent constructs 100 may be placed within the enclosed environment102. Alternatively, the sorbent constructs 100 may be placed out of theenclosed environment 102 and the indoor air 114 and/or the outside air124 may be introduced therein in any suitable manner.

The examples as set forth herein are meant to exemplify some of thevarious aspects of carrying out the disclosed embodiments and are notintended to limit the disclosure in any way.

The following examples 1, 2 and 3 describe methods for synthesizing theamine-containing support. It is appreciated that the amine-containingsupport may be composed in any suitable method.

EXAMPLE 1

Bentonite powder may be initially formed into particles, such asgranules or beads by any standard granulation method or may be formedinto pellets or extrudants by any standard pelletization or extrusionmethod.

In one embodiment the bentonite powder may be formed into high porosity,8-32 mesh acid treated bentonite pellets with a porosity of 20-500[m²/grams]

The granules or pellets may be dry sprayed by a liquid amine-basedcompound, such as diethanolamine (DEA), through a nozzle using a pump.The DEA may be solved by any suitable solvent such as by Dichloromethane(DCM). Additionally, a mixture of solved DEA and any other amine orcompound may be used. For example a mixture of DEA andtetraethylenepentamine (TEPA) with a 90:10 DEA to TEPA ratio may beused. In another example a 70:30 DEA to TEPA ratio may be used.

Alternately, the particles may be immersed in the liquid amine-basedsolution and thereafter dried. An amine impregnated bentonite mixture isformed.

The amine to clay ratio may vary, though the ratio is typically in therange of 30-50 grams of amine to 100 grams of clay.

A porosity agent, such as cellulose, may be added for enhancing theporosity of the particles. Another added porosity agent may be DRIERITE®commercially available from W.A. Hammond Drierite Co., Ltd.

The particles are used to form the amine-containing support.

EXAMPLE 2

A powder, such as bentonite powder with a porosity of 20-500 [m²/grams],may be dried by initially baking it at a temperature of 300-350° C. andthereafter at a temperature of 500-550° C. The dried powder may beplaced in a drum mixer. A liquid amine-based compound, such as solveddiethanolamine (DEA), may be sprayed through a nozzle using a pump whilecontinuously mixing the bentonite and amine-based compound mixture.Alternatively, the liquid amine-based compound may be slowly dripped onthe powder.

The DEA may be solved by any suitable solvent such as by Dichloromethane(DCM). Additionally, a mixture of solved DEA and any other amine orcompound may be used. For example a mixture of DEA andtetraethylenepentamine (TEPA) with a 90:10 DEA to TEPA ratio may beused. In another example a 70:30 DEA to TEPA ratio may be used.

Spraying or dripping should cease when the mixture is saturated and wetdrops start to form. The liquid to powder ratio may vary, though theratio is typically in the range of 30-50 grams of liquid to 100 grams ofpowder.

The amine impregnated bentonite powder mixture may or may not be furtherdried.

The amine impregnated bentonite powder is used to form theamine-containing support.

EXAMPLE 3

An amine impregnated bentonite powder is formed as described in example2.

The amine impregnated bentonite powder is formed into particles, such asgranules or beads by any standard granulation method or may be formedinto pellets or extrudates by any standard pelletization or extrusionmethod.

The particles are used to form the amine-containing support.

During performance of the processes described in examples 1-3 it isrecommended to refrain from overheating the amine impregnated bentonitemixture (such as to over than 100° C., for example) to prevent theevaporation of the amines.

In the following examples 4-8 adsorption and regeneration of differentexamples the sorbent 120 are described. The results of the describedexamples are shown in graphs of respective FIGS. 2-6. It is appreciatedthat other materials may be used to form the sorbent 120.

EXAMPLE 4

10 liters of solid supported amine granules were disposed into anenclosure. The solid supported amine granules comprised untreatedbentonite and an amine mixture of DEA and TEPA with a 90:10 DEA to TEPAratio. The solid supported amine granules were formed generallyaccording to the method of example 1.

Pressure sensors, temperature sensors and double (redundant) highaccuracy CO₂ sensors were placed both upstream and downstream of theenclosure.

Air at room temperature and standard humidity (48-52%) flowed throughthe sorbent at 40 Cubic Feet per Minute (CFM), with a CO₂ ofapproximately 1000 ppm.

The air exiting the sorbent contained a CO₂ concentration ofapproximately 200 ppm, representing about 75-80% efficiency in reducingthe CO₂ concentration in the air, as seen in FIG. 2. Therebydemonstrating rapid reaction kinetics. This efficiency was maintainedfor about 100 minutes at which point it began to slowly decline, asexpected, representing the gradual saturation of the sorbent.

The volume of CO₂ captured in the first two hours was estimated at 250grams, representing close to 3% of the 8 kG mass of the sorbent. In theabove adsorption cycle, which was allowed to continue even aftersaturation began, approximately 400 grams of CO₂ were adsorbed over thecourse of 3 hours, which is 5% of the sorbent's total mass.

Weighing the enclosure showed a weight increase of approximately 700grams, indicating about 300 grams of water adsorption in addition to CO₂adsorption. Importantly, it is noted, that the water was desorbedalongside the CO₂ and did not appear to have any detrimental effect onthe cyclical capacity to adsorb CO₂ and regenerate the sorbent and didnot appear to have any detrimental effect on the efficiency of thesorbent.

EXAMPLE 5

Following the adsorption of the CO₂, as described in example 4,regeneration of the sorbent was performed. Outdoor air was heated tovarious degrees during the regeneration cycle using an electric heaterplaced upstream the sorbent. The air temperature was heated toapproximately 40-70° C. and air was streamed at 40 CFM and 80 CFM. Thesorbent temperature was raised slowly over the course of 30 minutes to45-55° C. It was found that there was no need to raise the sorbent above55° C. at any point, and in fact it appeared that at 45° C. a very highrate of desorption was evident, as seen in FIG. 3.

Outgoing air, exiting the sorbent, reached a CO₂ concentration of over2000 ppm, an excellent result for such low temperatures and high flowrate. The CO₂ concentration began to drop within 15 minutes ofcommencement of the sorbent regeneration and continued to declinerapidly as the CO₂ was depleted from the sorbent.

EXAMPLE 6

0.8972 grams of solid supported amine granules were disposed into anenclosure. The solid supported amine granules comprised acid treatedbentonite and an amine mixture of DEA and TEPA with a 90:10 DEA to TEPAratio. The solid supported amine granules were formed generallyaccording to the method of example 1.

Air at a temperature of 40° C. and 3% moisture flowed through thesorbent at 50 Standard Cubic Centimeters per Minute (SCCM) for 60minutes, with a CO₂ concentration of approximately 1700 ppm.

As seen in FIG. 4, the CO₂ concentration generally continuously rose toapproximately 1800 ppm (i.e. 0.18%) after approximately 60 minutes,indicating continuous efficient CO₂ adsorption by the sorbent. Therebydemonstrating rapid reaction kinetics.

EXAMPLE 7

Following the adsorption of the CO₂, as described in example 6,regeneration of the sorbent was performed. A purge gas comprising 70 ccof N₂ was heated to 50° C. and streamed at 50 SCCM.

Outgoing purge gas, exiting the sorbent, reached a CO₂ concentration ofover 3800 ppm (i.e. 0.38%), an excellent result. The CO₂ concentrationbegan to drop within 8 minutes of commencement of the regeneration cycleand continued to decline rapidly as the CO₂ was depleted from thesorbent, as seen in FIG. 5.

EXAMPLE 8

0.8501 grams of amine-containing powder was disposed into an enclosure.The amine-containing powder comprised untreated bentonite and an aminemixture of DEA and TEPA with a 70:30 DEA to TEPA ratio. Theamine-containing powder was formed generally according to the method ofexample 2.

Air at a temperature of 40° C. and 4% moisture flowed through thesorbent at 15 SCCM for 250 minutes, with a CO₂ concentration ofapproximately 1700 ppm.

As seen in FIG. 6, the CO₂ concentration generally continuously rose toapproximately 1250 ppm (i.e. 0.125%) after approximately 240 minutes,indicating continuous efficient CO₂ adsorption by the sorbent. Therebydemonstrating rapid reaction kinetics

In accordance with some embodiments, the sorbent construct 100 may beprovided to reduce the CO₂ concentration as part of an air managementsystem, such as a Heating, Ventilation and Air-Conditioning (“HVAC”)system 104 (e.g., either integral therewith or an in-line componentthereof). In some embodiments, the HVAC system 104 is arrangeddownstream of the sorbent construct 100 as shown in FIG. 1, though otherarrangements of the HVAC system relative to the sorbent are within thescope of this disclosure. In air management systems the indoor airexiting the sorbent, following CO₂ reduction thereof, may berecirculated into an enclosed environment of the air management system.The sorbent of the sorbent construct 100 may repeatedly undergo anadsorption cycle for adsorbing the CO₂ and a regeneration cycle forregenerating the sorbent. Examples of removing substances from HVACsystems are disclosed in applicant's U.S. Pat. No. 8,157,892, which isincorporated herein by reference in its entirety.

It is noted that in accordance with some embodiments, the sorbentconstruct 100 described herein may be used for reduction of a substance,such as CO₂, from a first gas. The first gas may comprise air with a CO₂concentration in the range of 100-5000 ppm or any other concentration.

In accordance with some embodiments, the sorbent construct 100 may beregenerated by streaming a second or additional gas through the sorbent,wherein the second gas, prior to reduction of the substance, comprisesair with a CO₂ concentration of substantially less than 800 ppm belowthe CO₂ concentration in the first gas.

In accordance with some embodiments, the sorbent construct 100 may beused for reduction of CO₂ from a gas, comprising a solid support formedof a plurality of particles, wherein the particles are formed with adiameter in a range of substantially 0.1-10 millimeters. The support maybe impregnated by an amine-based compound comprising at least a 25% ofsecondary amines and being operable to capture the CO₂ for reductionthereof from the gas, which comprises a CO₂ concentration in the rangeof 100-2000 ppm.

Further features and advantages of the disclosed embodiments, as well asstructure and operation of various embodiments of the current subjectmatter, are disclosed in detail below with references to theaccompanying drawings.

Example embodiments of the methods and components of the current subjectmatter have been described herein. As noted elsewhere, these exampleembodiments have been described for illustrative purposes only, and arenot limiting. Other embodiments are possible and are covered by thecurrent subject matter. Such embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.Thus, the breadth and scope of the current subject matter should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A sorbent for reduction of CO₂ from indoor air ofan enclosed space, comprising: a plurality of solid particles having anaverage diameter dimension in the range of 0.1-10 millimeters, andwherein at least some of the particles comprise: a support material; andan amine-based compound, wherein at least 25% of amine functional groupsare secondary amines, wherein the amine-based compound further compriseswater, wherein the support is combined with the amine-based compound;and wherein the amine-based compound is configured to capture at leastsome of the CO₂ within the indoor air of the enclosed space and releaseat least a portion of the captured CO₂.
 2. A sorbent according to claim1, wherein the support is selected from the group consisting of gels,molecular sieves, nanotube-containing materials, porous materials,sponge and sponge-like materials, electro-magnetically charged objects,porous organic polymers, ion exchange resins, polymeric absorbentresins, acrylic ester polymers, polystyrene divinyl benzene, polymethylmethacrylate (PMMA), polystyrene, styrene divinylbenzene (SDB), fly ash,activated carbon, carbon nanotubes, alumina nanoparticles, syntheticzeolite, porous alumina, porous minerals, porous silica, silicananoparticle, fumed silica, activated charcoal, aluminumphyllosilicates, bentonite, montmorillonite, ball clay, fuller's earth,kaolinite, attapulgite, hectorite, palygorskite, saponite,sepiolitemetal, organic frameworks, and any combination thereof.
 3. Asorbent according to claim 1, wherein the support comprises a pluralityof particles with an average diameter dimension in the range of 0.2-3millimeters.
 4. A sorbent according to claim 1, wherein the supportcomprises a plurality of particles with an average diameter dimension inthe range of 0.3-1 millimeters.
 5. A sorbent according to claim 1,wherein the support is selected from the group consisting of granules,beads, pellets, extrudates, and any combination thereof.
 6. A sorbentaccording to claim 1, wherein at least 50% of amine functional groups ofthe amine-based compound are secondary amines.
 7. A sorbent according toclaim 1, wherein the amine-based compound comprises monoethanolamine(MEA), ethanolamine, methylamine, branched polyethyleneimine (PEI),linear polyethyleneimine (PEI), diethanolamine (DEA), dimethylamine,diethylamine, diisopropanolamine (DIPA) tetraethylenepentamine (TEPA),methyldiethanolamine (MDEA), methylethanolamine, or any combinationthereof.
 8. A sorbent according to claim 1, wherein the supportcomprises particles, fine particles, or a powder based solid; whereinthe fine particles are agglomerated into larger particles, so as tofacilitate air flow through the sorbent.
 9. A sorbent of claim 1,wherein the support is impregnated by the amine-based compound withadditional mechanical stimulation, catalysts, or external energysources, such as heat.
 10. A sorbent for reduction of CO₂ from air of anenclosed space, comprising: a support comprising a plurality of solidparticles having an average diameter dimension in the range of 0.1-10millimeters; and an amine-based compound comprising a polyamine havingbetween 25%-75% of secondary amines and water, and wherein theamine-based compound is configured to capture at least some of the CO₂within the indoor air of the enclosed space and release at least aportion of the captured CO₂ by streaming air or other gas through thesorbent.
 11. A sorbent according to claim 10, wherein the support isselected from the group consisting of gels, molecular sieves,nanotube-containing materials, porous materials, sponge and sponge-likematerials, electro-magnetically charged objects, porous organicpolymers, ion exchange resins, polymeric absorbent resins, acrylic esterpolymers, polystyrene divinyl benzene, polymethyl methacrylate (PMMA),polystyrene, styrene divinylbenzene (SDB), fly ash, activated carbon,carbon nanotubes, alumina nanoparticles, synthetic zeolite, porousalumina, porous minerals, porous silica, silica nanoparticle, fumedsilica, activated charcoal, aluminum phyllosilicates, bentonite,montmorillonite, ball clay, fuller's earth, kaolinite, attapulgite,hectorite, palygorskite, saponite, sepiolitemetal, organic frameworks,and any combination thereof.
 12. A sorbent according to claim 10,wherein the support is selected from the group consisting of granules,beads, pellets, extrudates, and any combination thereof.
 13. A sorbentaccording to claim 10, wherein at least 50% of amine functional groupsof the amine-based compound are secondary amines.
 14. A sorbentaccording to claim 10, wherein the amine-based compound comprisesmonoethanolamine (MEA), ethanolamine, methylamine, branchedpolyethyleneimine (PEI), linear polyethyleneimine (PEI), diethanolamine(DEA), dimethylamine, diethylamine, diisopropanolamine (DIPA)tetraethylenepentamine (TEPA), methyldiethanolamine (MDEA),methylethanolamine, or any combination thereof.
 15. A method forreducing CO₂ contained in air from an enclosed environment, the methodcomprising: providing a sorbent comprising a support including aplurality of solid particles having an average diameter dimension in therange of 0.1-10 millimeters; and an amine-based compound comprising apolyamine having between 25%-75% of secondary amines and water,streaming a first gas comprising CO₂ from inside an enclosed environmentthrough the sorbent such that the sorbent captures at least some of theCO₂ from the first gas; and streaming a second gas through the sorbentsuch that the sorbent releases at least some of the captured CO₂ to thesecond gas.
 16. The method of claim 15, wherein the second gas comprisesless CO₂ than the first gas.
 17. The method of claim 15, wherein thesecond gas has a temperature higher than the first gas.
 18. The methodof claim 15, wherein the second gas is heated prior to streaming thesecond gas through the sorbent.
 19. The method of claim 15, wherein thesecond gas comprises outdoor air from outside the enclosed environment.20. The method of claim 15, wherein the second gas comprises indoor airfrom inside the enclosed environment.